1. Field of the Invention
The present invention relates to a vibration damper with a fluid filled therein.
2. Description of the Relevant Art
One known fluid-filled vibration damper has a partition plate disposed in a fluid-filled chamber and slightly movable in transverse directions thereof for absorbing vibrations of small amplitudes. Such a fluid-filled vibration damper is shown in FIG. 8 of the accompanying drawings. The fluid-filled vibration damper has a fluid chamber 100 defined between an elastomeric member 140 and a diaphragm 160 and filled with a fluid, The fluid chamber 100 is divided by a partition 130 into a first fluid chamber 101 and a second fluid chamber 102. The partition 130 is movable a small distance in transverse directions thereof (vertically in FIG. 8) between upper and lower stops 103, 104 which limit the transverse movement of the partition 130. The vibration damper has an attachment 110 attached to a vibration source such as an engine, and a base 120 attached to a structural member such as a vehicle body Vibrations of small amplitudes which are transmitted from the vibration source are absorbed by vertical oscillation of the partition 130 between the upper and lower stops 103, 104. When the vibration source vibrates with large amplitudes, the fluid flows through an orifice 150 through which the first and second fluid chambers 101, 102 communicate with each other, for producing damping forces.
When a motor vehicle with the above fluid-filled vibration damper used as an engine mount runs on a road having a continuous spread of relatively small surface irregularities, the attachment 110 is repeatedly vibrated with amplitudes exceeding a certain level in response to vertical movement of the motor vehicle. Such repeated vibration of the attachment 110 beyond the certain amplitude level causes the partition 130 to vibrate vertically. Since the rate of flow of the fluid through the orifice 150 is lowered by the vertical movement of the partition 130, the vibration damper cannot produce sufficient damping forces. Therefore, the vibrations generated while the motor vehicle is running on a bumpy road.